1. Field of the Invention
The invention relates to a fixturing device for holding a substrate or array of substrates, and more particularly, the invention relates to a fixturing device for holding the substrates and allowing liquids to effectively drain from the substrates"" surfaces.
2. Brief Description of the Related Art
A Substrates as used for manufacturing various advanced technology microelectronic devices and mass data storage components require increasingly stringent cleaning requirements. Typically, substrates are processed by using wet immersion cleaning techniques which involve a series of liquid baths whereby an operator loads the substrates into wafer carriers and dips the carriers into liquid processing bathes. After the bathing process completes, the carrier is lifted out of the bath and carried to the next process. However, liquid may adhere to the substrate surfaces or accumulate in the contact areas between the carrier and substrates which results in cross-contamination problems when the wafer carrier enters the next process. Further, contact surfaces between the carrier and substrates are not exposed during the cleaning process and thus not processed, thereby reducing the amount of substrate surface area usable for manufacturing microelectronic and data storage devices. Other critical issues in wet process cleaning are foreign particles, residue or stains, and substrate handling damage.
Known substrate fixturing devices utilize slots or notches to support the substrates, and spacing between the slots separates the substrates so that both substrate surfaces are exposed. These slots or notches may retain liquid or cleaning solution after completing a bath process, and such retained liquid or cleaning solution adhering to the fixturing device or substrate surface may contaminate a subsequent cleaning tank. Substrate fixturing devices utilized in an air or nitrogen drying process must draw liquids away from the substrate and provide a design capable of quickly drying any remaining liquid on the fixturing device, itself. Moreover, conventional wafer carriers require a plurality of substrate fixturing devices to support the substrates or wafers.
One example of a substrate holder is disclosed in U.S. Pat. No. 5,704,493 to Fujikawa, et al. This substrate holder includes a parallel arrangement of bridges affixed to a pair of frames, whereby each bridge has an alternate arrangement of teeth and valleys. The valleys between the teeth are Y-shaped or V-shaped notches in which substrates may be held, contacting only the vertical notch walls. Cylindrical vent holes formed in the bottoms of the notches provide drainage for processing liquids, or aqueous cleaning solutions, when the substrate holder is lifted out of a bathing or rinsing tank. The processing liquid present on the notches drains by gravity through the vent holes, and only a small amount of processing liquid remains in the straight portion of each vertical notch. Although the Fujikawa substrate holder allows for drainage of processing liquid, capillary action due to surface tension, cohesion of the liquid molecules, and the adhesion of the molecules on the surface of a straight cylindrical solid will prevent complete evacuation of processing liquid through the cylindrical vent holes. Moreover, the Fujikawa substrate holder assembly requires the use of at least three plates to support the parallel array of substrates.
Another example of a wafer carrier is disclosed in U.S. Pat. No. 4,993,559 to Cota. This wafer carrier includes side rails and a bottom rail with slots of sufficient width for holding the lateral edges of a wafer. Additional rails reenforce and hold the side and bottom rails in appropriate positions. The side rails have slots that are inclined at an angle with respect to the vertical such that a wafer leaning in a side slot rests substantially against a corner in the side rail slot. The bottom slots have a curved floor, convex upward, for supporting a wafer edge rather than a wafer corner, thereby substantially decreasing the probability that the wafer will become chipped when inserted or removed from the wafer carrier. While the Cota wafer carrier minimizes the contact area of the wafer edge with the rail slots, the side and bottom slots do not allow processing liquids to drain, and the slots and rails retain moisture. Like the Fujikawa substrate holder, multiple rails are required to support the wafers.
Yet another example of a wafer boat is disclosed in U.S. Pat. No. 5,534,074 to Koons. This wafer boat includes vertically extending rods mounted to a base, and each vertical rod has slots with peaked surfaces, rather than flat surfaces. The peaked surface forms an inverted V-shape and provides minimal contact between the rods and the wafers. Wafers slide into the slots and rest on the apexes of the peaked surfaces. While this arrangement may minimize wafer surface contact, it does little to accommodate for down-draft drying ventilation typically used in drying processes.
The present invention relates to a substrate fixturing device which supports an array of substrates during various processing steps, including but not limited to cleaning, drying, and coating of the substrates.
Generally speaking, the present invention provides a substrate fixturing device that supports the substrates during the various cleaning steps while draining away liquid, such as cleaning solution, retained by the fixturing device and the substrate surfaces between process steps to prevent cross-contamination of process vessels. In the present invention, by minimizing the contact surfaces between the carrier and substrates, most of the substrate surface is exposed during the cleaning process, thereby maximizing the amount of substrate surface area usable for manufacturing microelectronic and data storage devices.
In accordance with one aspect of the present invention, a substrate fixturing device utilizes peaked converging surfaces to minimally, yet firmly, contact and support the substrates in vertical notches so that a maximum surface area is exposed during cleaning processes or during air or nitrogen drying processes. The peaked converging surfaces support the substrate and enhance the drawing of liquid through passages away from the fixturing device and the substrate surfaces by gravity or by forced air or nitrogen during the drying process, thereby preventing the substrate supporting slots and fixturing device from retaining moisture. In conjunction, the passages allow the processing liquid to evacuate the fixturing device and prevents the liquids from pooling and staining the substrate at the bottom of the notches. The passages have a converging-diverging contour that, like the peaked converging surfaces, enhance the drawing of liquid away from the fixturing device and the substrate surfaces by gravity and forced air, as well as counters capillary action due to surface tension, cohesion of the liquid molecules, and the adhesion of the molecules on the surface of the fixturing device.
The present invention provides advantages of supporting substrates using a singular piece substrate fixturing device while minimizing the contact surfaces between the fixturing device and the substrates so that most of the substrate surface is exposed during the cleaning, drying, or coating processes. The passages and the pair of peaked converging supporting surfaces in the substrate supporting slots assist in the drawing away and drying of moisture present on the fixturing device.
In particular, the present invention provides a fixturing device which supports a substrate or a plurality of substrates in a vertical orientation during cleaning, drying, and coating processing steps while minimizing the contact surfaces between the fixture and each substrate so that a maximum of the substrate surface is exposed. The fixturing device utilizes converging support surfaces that terminate at the closest point in a gap with a distance less than the thickness of a substrate. The converging support surfaces counter surface tension, cohesion of the liquid molecules, and the adhesion of the liquid molecules on the surface of the fixturing device. The gap in the converging support surfaces prevents the fixturing device from retaining liquid at the interface of the substrate and the fixture. In conjunction, the contoured passages enhance the drawing of liquid away from the fixturing device and prevents pooling and staining the substrate. This fixturing device can be implemented in plurality to form two or three dimensional arrays to support a plurality of substrates. The fixturing device can be designed to interface with substrates through an internal aperture, an outer perimeter, or as an end effector on a gripper.